1. Technical Field
The present invention relates to a light guide apparatus that can be used in a virtual image display apparatus that presents a viewer with video images formed, for example, by an image display apparatus and further relates to a virtual image display apparatus using the light guide apparatus.
2. Related Art
A variety of optical systems have been proposed as a video light guiding optical system incorporated into a virtual image display apparatus, such as a head mounted display (hereinafter also referred to as HMD) mounted on a viewer's head (see JP-T-2003-520984, the term “JP-T” as used herein means a published Japanese translation of a PCT patent application).
As a virtual image display apparatus of this type or a light guide apparatus suitable for the virtual image display apparatus, for example, there is a known apparatus using a reflection member having the shape of a Fresnel lens (the shape is hereinafter referred to as a Fresnel shape) formed by arranging, along a flat surface, a plurality of prism-shaped members each having a small flat reflection surface (see JP-T-2003-520984).
An HMD and other virtual image display apparatus are required to be further reduced in size with the optical accuracy maintained. To this end, using a Fresnel-shaped member, such as the member described above, to guide light allows reduction in the thickness of a light guide optical system and hence reduction in the size of an apparatus. However, when light passes through such a Fresnel-shaped member (see FIGS. 7A to 9 of JP-T-2003-520984, for example), for example, the light is dispersed due to the difference in refractive index between the member and an air layer or between the member and another member bonded thereto, possibly resulting in image deterioration.